Port flexible_event_privacy.py to TypeScript (#917)

This will allow us to incorporate this information into the header
validator.

Co-authored-by: Charlie Harrison <[email protected]>

flexible-event/.gitignore

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+dist
+node_modules

flexible-event/README.md

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+Setup:
+
+```sh
+npm install && npm run tsc
+```
+
+Examples:
+
+```sh
+npm run main -- -w 1,2,3 -b 4,5,6
+```
+
+```sh
+npm run main -- -f /path/to/source_registration.json
+```

flexible-event/main.ts

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+const commandLineArgs = require('command-line-args')
+const fs = require('fs')
+
+import {Config, DefaultConfig, PerTriggerDataConfig, SourceType} from './privacy'
+
+function commaSeparatedInts(str: string): number[] {
+  return str.split(',').map(v => Number(v))
+}
+
+function parseSourceType(str: string): SourceType {
+  if (!(str in DefaultConfig)) {
+    throw 'unknown source type'
+  }
+  return str as SourceType
+}
+
+function getNumWindowsFromJson(defaultVal: number, windows?: object): number {
+  if (typeof windows === 'undefined') {
+    return defaultVal
+  }
+
+  if (typeof windows !== 'object') {
+    throw 'event_report_windows must be an object'
+  }
+
+  const endTimes = windows['end_times']
+  if (!Array.isArray(endTimes)) {
+    throw 'end_times must be an array'
+  }
+
+  return endTimes.length
+}
+
+function getConfig(json: object, sourceType: SourceType): Config {
+  const defaultMaxReports = DefaultConfig[sourceType].maxEventLevelReports
+  const defaultWindows = defaultMaxReports
+
+  let maxEventLevelReports = json['max_event_level_reports']
+  if (typeof maxEventLevelReports === 'undefined') {
+    maxEventLevelReports = defaultMaxReports
+  } else if (typeof maxEventLevelReports !== 'number') {
+    throw 'max_event_level_reports must be a number'
+  }
+
+  const topLevelNumWindows = getNumWindowsFromJson(defaultWindows, json['event_report_windows'])
+
+  const triggerSpecs = json['trigger_specs']
+  if (!Array.isArray(triggerSpecs)) {
+    throw 'trigger_specs must be an array'
+  }
+
+  const perTriggerDataConfigs: PerTriggerDataConfig[] = []
+  triggerSpecs.forEach((spec: object) => {
+    const triggerData = spec['trigger_data']
+    if (!Array.isArray(triggerData)) {
+      throw 'trigger_data must be an array'
+    }
+
+    const numDataTypes = triggerData.length
+
+    const numWindows = getNumWindowsFromJson(topLevelNumWindows, spec['event_report_windows'])
+
+    // Technically this can be larger, but we will always be constrained
+    // by `max_event_level_reports`.
+    let numBuckets = maxEventLevelReports
+    const summaryBuckets = spec['summary_buckets']
+    if (typeof summaryBuckets !== 'undefined') {
+        if (!Array.isArray(summaryBuckets)) {
+          throw 'summary_buckets must be an array'
+        }
+        numBuckets = summaryBuckets.length
+    }
+
+    for (let i = 0; i < numDataTypes; i++) {
+      perTriggerDataConfigs.push(new PerTriggerDataConfig(numWindows, numBuckets))
+    }
+  });
+
+  return new Config(maxEventLevelReports, perTriggerDataConfigs)
+}
+
+const optionDefs = [
+  {
+    name: 'max_event_level_reports',
+    alias: 'm',
+    type: Number,
+    defaultValue: 20,
+  },
+  {
+    name: 'epsilon',
+    alias: 'e',
+    type: Number,
+    defaultValue: 14,
+  },
+  {
+    name: 'source_type',
+    alias: 't',
+    type: parseSourceType,
+    defaultValue: SourceType.Navigation,
+  },
+  {
+    name: 'windows',
+    alias: 'w',
+    type: commaSeparatedInts,
+  },
+  {
+    name: 'buckets',
+    alias: 'b',
+    type: commaSeparatedInts,
+  },
+  {
+    name: 'json_file',
+    alias: 'f',
+    type: String,
+  },
+]
+
+const options = commandLineArgs(optionDefs)
+
+let config: Config
+if ('json_file' in options) {
+  const json = JSON.parse(fs.readFileSync(options.json_file, {encoding: 'utf8'}))
+  config = getConfig(json, options.source_type)
+} else {
+  if (options.windows.length != options.buckets.length) {
+    throw 'windows and buckets must have same length'
+  }
+  config = new Config(
+    options.max_event_level_reports,
+    options.windows.map((w, i) => new PerTriggerDataConfig(w, options.buckets[i])),
+  )
+}
+
+const out = config.computeConfigData(options.epsilon, options.source_type)
+
+console.log(`Number of possible different output states: ${out.numStates}`)
+console.log(`Information gain: ${out.infoGain.toFixed(2)} bits`)
+console.log(`Flip percent: ${(100 * out.flipProb).toFixed(5)}%`)
+
+if (out.excessive) {
+  const e = out.excessive
+  console.log(
+      `WARNING: info gain > ${e.infoGainDefault.toFixed(2)} for ${options.source_type} sources. Would require a ${(100 *
+        e.newFlipProb).toFixed(5)}% flip chance (effective epsilon = ${e.newEps.toFixed(3)}) to resolve.`)
+}